Ferromagnetism in Hubbard models with nearest-neighbor Coulomb repulsion

Hiroki Nakano, Yoshinori Takahashi

Metal–insulator transition in the ground state of the Hubbard chain with the next-nearest-neighbor hopping is studied by exact diagonalization method. This model shows the partially ferromagnetic metal near the Mott insulator for large Coulomb repulsion while the model reveals the non-magnetic metal for small but finite Coulomb repulsion. We find the transition between the partially ferromagnetic metal and the Mott insulator without phase separation. A new critical exponent of the diverging charge compressibility with respect to the hole density is observed when the system approaches the metal–Mott-insulator transition point from the side of the partially ferromagnetic metal. We also find the occurrence of the phase separation between partially ferromagnetic metal and the Mott insulator for even larger Coulomb repulsion. The model proposed here is interesting in view of the magnetism as well as the metal–insulator transition.

Wolfgang Nolting, Michael Potthoff, T. Herrmann +1 more

Andreas Mielke, Hal Tasaki

David K Campbell, J. Tinka Gammel, Eugene Loh

We investigate the general applicability of the standard Peierls-Hubbard model, involving both on-site ($U$) and nearest-neighbor ($V$) Coulomb repulsions, by adding nearest-neighbor off-diagonal terms representing the bond ($W$) and mixed bond-site ($X$) electron-electron repulsive interactions. For a broad range of the site-diagonal Hubbard parameters ($U,V$), we find that the off-diagonal terms ($W,X$) initially enhance dimerization, thereby stabilizing the dimerized ground state.

Harumi Sakamoto, Ken Kubo, 坂本 晴美 +1 more

Hiroki Nakano, Yoshinori Takahashi

We study the one-dimensional Hubbard model with next-nearest-neighbor hopping by means of the numerical diagonalization for finite-size clusters. It is found that the ground state is evidently partially spin-polarized in a wide region of intermediate values of on-site Coulomb repulsion, which provides the first example as a minimal model without orbital degeneracy. Analysis of correlation functions makes it clear that the partially spin-polarized states form a spin polaron. Polaron's size grows with the increasing interaction.